Titrations in non-aqueous media. Part XI. Basicities of open-chain and cyclic polyether derivatives of aniline

Abstract

Aniline and a number of its open-chain and cyclic polyether derivatives were titrated potentiometrically in nitrobenzene solvent and their pK_a′ values calculated. Examination of the pK_a′ values revealed that all the polyether derivatives of aniline are more basic than aniline itself. In the open-chain polyether derivatives, a linear relationship was observed between the first pK_a′ values and the number of ether oxygen atoms (separated from each other by the ethylene or propylene groups). An identical relationship was observed for the cyclic polyether derivatives of aniline. The cyclic polyethers were also found to be more basic than the corresponding open-chain polyethers. However, the latter were more susceptible to protonation than the corresponding cyclic polyethers. Although the titration curves of the open-chain polyethers containing three and four ether oxygen atoms showed two end-points, the titration curves of the corresponding cyclic polyethers showed only one end-point. As regards basicity or acidity, an inductive effect usually propagates six bonds along at most, but in the compounds studied it propagated at least 16 bonds along. In these compounds, each ether oxygen atom could transmit the inductive effect along the open- or cyclic-chain.